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ABSTRACT

A PRIMARY AND SECONDARY ELECTROCHEMICAL CELL WHICH COMPRISES IN COMBINATION AN ANODE OF AMETAL CAPABLE OF REDUCING A CATHODE DEPOLARIZER, SULFUR DIOXIDE ALONE OR IN A CO-SOLVENT, AN ELECTROLYTE SALT, AND SOLUBLE DEPOLARIZERS.

United States Patent Office Re. 27,835 Reissued Dec. 11, 1973 27,835NONAQUEOUS ELECTROCHEMICAL CURRENT PRODUCING CELL HAVING SOLUBLE CATH-ODE DEPOLARIZER Donald Leonard Maricle, Ridgefield, and Arthur KentaroHolfmann, New Canaan, Conn., by American Cyanamid Company, Stamford,Conn., assignee No Drawing. Original No. 3,578,500, dated May 11, 1971,Ser. No. 743,005, July 8, 1968. Application for reissue Nov. 29, 1971,Ser. No. 203,083

Int. Cl. H01m 17/00 U.S. Cl. 136-6 LN 8 Claims Matter enclosed in heavybrackets [II appears in the original patent but forms no part of thisreissue specification; matter printed in italics indicates the additionsmade by reissue.

ABSTRACT OF THE DISCLOSURE A primary and secondary electrochemical cellwhich comprises in combination an anode of a metal capable of reducing acathode depolarizer, sulfur dioxide alone or in a co-solvent, anelectrolyte salt, and soluble depolarizers.

This invention relates to electrochemical cells and batteries. Moreparticularly, this invention relates to nonaqueous primary and secondaryelectrochemical cells and batteries having a novel and improved cathodedepolarizer system which incorporates soluble depolarizers.

Cathode depolarizers are conventionally employed in a form which willpermit intimate and maximum contact with an external electrical conduit,such as the wires connecting the electrodes of a cell or battery, whilealso effecting separation of the cathode depolarizer from the anode.Thus, in practice, the cathode depolarizer is generally an insoluble,finely divided solid admixed with or plated over an inert conductingmaterial such as nickel, graphite or carbon rod. The mechanicalseparation of the cathode depolarizer material from the anode isnecessary to prevent the chemical reaction of cathode depolarizer withanode material which, in effect, would discharge the battery internallywithout doing any useful work. For example, in the common Leclanchecell, the anode is zinc metal, the cathode is a porous carbon pencil,the cathode depolarizer is a mixture of manganese dioxide and acetylenecarbon black, and the electrolyte is a mixture of ammonium chloride andzinc chloride gelled to a paste with corn starch and wheat flour. Thecathode depolarizer mix is generally pressed around the carbon pencilwhich is centered in a cylindrical zinc anode casing and the electrolytepaste fills the cylindrical space between cathode depolarizer mix andouter zinc casing. Separation of cathode depolarizer and zinc anode ismaintained by the essentially solid state of the cathode depolarizermixture, by the electrolyte paste and by a separator of paper or similarmaterial.

As examples of other cells requiring separation of anode and cathodedepolarizer may be mentioned the mercury dry cell (HgO cathodedepolarizer with 2110- saturated KOH electrolyte and oellulosicseparator), alkaline manganese dry cell (zinc/KOH/Mno zincmercury-carbon cell (mercury dioxysulfate as cathode depolarizer withspecial gel-coated separator next to the surrounding zinc can), andalkaline silver-zinc dry cell (similar to mercury cell but with Ag O rAgO instead of HgO). In each of such cells the cathode depolarizermaterial is a solid which is finely distributed in a matrix to obtainthe greatest possible surface area for optimum electrical contact,conductivity and reduction. The solid state of this material also servesto separate the anode from the cathode mix so as to eliminate orsubstantially reduce interaction with the anode. Mechanical separationis conventionally further enhanced by employing the cathode depolarizeras a powder, compact, compartmentalized solution or suspension, platingor glossy metal oxide film, and by utilizing a separator material suchas starch paste, fibrous material such as cotton, dacron and nylon,alone or impregnated with resins, gels and the like.

Attempts have been made to modify such cells by the use of more activemetals as anodes because of their higher potentials. However, in thecase of active metals such as aluminum and magnesium, the electrolytesmust be varied to control attack on these metals. It will be evidentthat a cell which not only eliminates the need for chemical separationof anode and cathode depolarizer but also utilizes an active metal suchas lithium, sodium, potassium, aluminum or magnesium as the anode,without attack by cathode depolarizer or electrolyte, would provide highperformance (watt-hours per pound) at minimum expense.

An object of the present invention is to provide a new and improvedprimary or secondary cell which avoids the need for chemical separationof cathode depolarizer and anode.

A further object of the present invention is to provide low cost primaryand secondary cells and batteries producing higher watt-hours per poundwhen used with preferred active anode materials such as lithium andsodium.

Another object is to provide a cell employing a nonaqueous system andutilizing soluble depolarizers.

These and other objects and advantages of the present invention will beapparent from the detailed exposition which follows.

[In our previous application, Ser. No. 678,476, filed Oct. 10, 1967, nowabandoned and continued in Ser. No. 782,768, filed Dec. 10, 1968, nowabandoned, we]

In previous applications which resulted in US. Pat. No. 3,567,515,patented Mar 2, 1971, there was disclosed an electrochemical cell whichin its essential form comprised an anode of a metal capable of reducingsulfur dioxide, a cathode of a material substantially inert to sulfurdioxide but on which sulfur dioxide is reducible, said anode and cathodebeing immersed in a mixture of sulfur dioxide solution and anelectrolyte salt substantially inert to sulfur dioxide and to the anodemetal, wherein the sulfur dioxide solution was used as the cathodedepolarizer.

We have now discovered that certain soluble compounds may be used asdepolarizers instead of, or together with, sulfur dioxide. In eithercase, sulfur dioxide is employed as the solvent or as a cosolvent.Suitable soluble depolarizers are electroactive compounds having arelatively large size and having solubility in the cell electrolytesystem (electrolyte, sulfur dioxide and solvent, and being inertthereto, and having a redox potential at least equal to or moreoxidizing than sulfur dioxide. The depolarizers may be soluble in eitherthe oxidized or reduced or both states and should have a solubility inthe electrolyte system of at least 10 molar.

Various compounds are suitable such as aromatic amines, particularlytertiary aromatic amines, quinones, metal complexes of organic compoundsand inorganic compounds. Such compounds include, for example, N,N,N',N'-tetramethyl benzidine: N.N,N',N'-tetrametl1yldiimoniumdiphenoquinone diperchlorate: LZ-bis-julodinium ethylenediperchlorate; the tetra cation of N,N,N',N'- tetrakis (p diethylaminophenyl)-p-phenylenediamine; l,10 phenanthroline ferrous perchlorate;bis-(ditrifluoromethyl ethylene dithiolato) No";tris-(ditrifluoromethylene ethylene dithiolato) Cr";bis-(ditrifiuorornethyl ethylene dithiolato) Co; tetracyano ethylene;sulfuryl chloride; and the like.

By sulfur dioxide solution is meant liquid sulfur dioxide(superatmospheric pressure or low temperature system) or a liquidcosolvent admixed with, e. g., substantially saturated by, gaseoussulfur dioxide at atmospheric pressure, or systems comprising mixturesof sulfur dioxide and cosolvent wherein the sulfur dioxide issubstantially in excess, i.e., wherein the sulfur dioxide is the primarysolvent, at superatmospheric pressure.

The anode is a metal or metallic material which is capable of reducingsulfur dioxide, i.e., the metal ion has less tendency than sulfurdioxide to accept electrons. Stated otherwise, the anode is any metalWhose oxidized form is not reduced by the reduced form of sulfur dioxideor is a metal which exhibits a standard electrode potential(Gibbs-Stockholm electrode potential relative to the standard hydrogenelectrode-SHE) greater, i.e., more reducing or less "noble, than that ofsulfur dioxide. Particularly preferred is any metal which has a standardelectrode potential of at least 0.2 volt more negative than that ofsulfur dioxide in the non-aqueous systems herein described. Suchstandard electrode potentials conform to techniques of determination andsign convention having almost universal acceptance in the art asendorsed by the International Union of Pure and Applied Chemistry (1953)and as detailed in the Encyclopedia of Electrochemistry, ReinholdPublishing Company (1964), pages 429-431.

Suitable metals are those substantially inert to sulfur dioxide, i.e.,do not chemically react with sulfur dioxide beyond formation of apassivating film on the surface of the metal nor do they substantiallyphysically react with sulfur dioxide during the useful life of thebattery so as to be dissolved, disintegrated or dispersed. By apassivating film is meant some form of metal-sulfur dioxide complex orreaction product (not wholly identifiable) which prevents substantialfurther attack of sulfur dioxide on the metal anode and chemical orphysical (except electrochemical) interaction of anode metal with theelectrolyte solution and soluble depolarizers contained therein.

This passivation is one of the unique advantages of the presentinvention since it permits elimination of the conventional separator orbarrier between anode and cathode depollarizer. In addition, thepassivating film operates in a manner similar to a conventionalsemi-permeable membrane since it remains porous to anodic ions and thusdoes not substantially impede the charge and discharge (electrochemicalreduction and oxidation) of the anode metal.

Preferred anode metals are lithium, sodium, potassium and the alkalineearth metals such as beryllium, magnesium, calcium, strontium andbarium. Of the foregoing, particularly preferred are lithium and sodium.Due to their activity and low equivalent weight, lithium and sodiumprovide the highest performance in watt-hours per pound weight of cellof all known materials. Moreover, these metals are substantially inertto sulfur dioxide and are passivated by sulfur dioxide as explainedabove. Less preferred metals are rubidium, cesium, aluminum andtransition metals having reduction potentials in a non' aqueous systemmore negative than sulfur dioxide such as zinc, tin, manganese,chromium, gallium, indium and the like. It will be appreciated that theforegoing metals may be employed alone, in mixtures or alloys of two ormore, or in other forms such as powders and compacts alone or over aconducting or semi-conducting substrate.

Cathode depolarizers in a secondary battery must have certain desirablecharacteristics. They must (1) undergo rapid, reversible electrontransfer so as to minimize polarization and overvoltage (2) have longterm compatibility with the other components of the battery and (3) haveas high a potential and as low an equivalent weight as is practicablypossible. Other requirements are imposed on the cathode depolarizer bythe particular battery system employed. In most batteries, the cathodedepolarizer m st be insoluble in order to prevent direct chemicalreaction with the anode (self discharge). Such reaction would lead to alower operating potential as well as to a loss in capacity and shelflife. Because of the passivating film formed on lithium in an 50;,containing solvent it is possible to employ a soluble cathodedepolarizer without deterioration of the battery. The existence of thisfilm, therefore, allows a much wider choice of oxidants since solublematerials are permitted. In fact, the use of a completely solublecathode depolarizer has some advantages.

In order to provide electrical contact to an insoluble, generallynon-conductive depolarizer, it is necessary to suspend it in aconductive matrix. Mass transport in the solid becomes a problem andmost of the successful depolarizers are at least partially conductive.The use of a conductive matrix not only increases the effective cathodeweight but also imposes the requirement of mechanical reversibility onthe cathode. If after a discharge-charge cycle the structure of thecathode is significantly changed, the capacity of the battery as well asthe ultimate lifetime will be reduced. These problems do not arise withan ideal soluble depolarizer, where both the oxidized and reduced formsare highly soluble. The major problem in this instance is diffusion ofthe depolarizer to the cathode surface where it is reduced and diffusionof the reduction product away from the cathode. In other words both thedepolarizer and its reduction product must have sufiiciently highmobility so that concentration polarization of the battery is relativelylow at reasonable drain rates. The depolarizer may however be soluble inonly one of the oxidized or reduced states. Thus, the solubledepolarizer concept is an extremely valuable one since a much greaterlatitude is allowed in the choice of potentially useful molecules.

The electrode is an integral part of the system and the properties ofthe depolarizer influence the type of electrode which must be employed.As mentioned above, the solubility properties of the depolarizer areimportant in determining the design of the cathode. If the solubility ofthe oxidized and reduced forms of the depolarizer are different, thecathode must accommodate this difference. The electrochemical propertiesof the cathode substrate are also important. The cathode substrateshould be chemicallly inert in the potential range required in theoperation of the cathode.

Cathode design may be either of two types depending on the solubility ofthe depolarizer and its reduction product formed during discharge of thecathode.

When both forms of the depolarizer are soluble the cathode material andits form are non-critical. In this case, the depolarizers may simply beadded to the battery solution. The material of the cathode may be anywhich serves as a conductor of electrons and which is substantiallyinert to sulfur dioxide and to the depolarizer, i.e., which serves totransmit electrons to the depolarizer acting as an electron acceptor oroxidizing agent (in the sense of electron acceptor and not as donor ofoxygen atoms to the cathode material by chemical reaction). Bysubstantially inert is meant the substantial absence of chemical orphysical (except electrochemical) interaction of the material with thedepolarizer such as chemical oxidation, physical disintegration,dissolution, precipitation or coagulation during the useful life of thebattery.

Preferred cathode materials for such soluble cathode product cells aremetals of the platinum family including platinum, iridium, osmium,palladium, rhodium and ruthenium; carbon in any of its common electrodeforms such as sintered, compacted or powdered graphite or carbon rod,alone or over platinum; iron in various forms, particularly as stainlesssteel; and nickel, silver, mercury, lead and gold. Less preferredmaterials are metals of the families of titanium, vanadium, chromium,manganese and iron (Groups IV B, V B, V] B, VIII B, and VIII of thePeriodic Table); in alloys: copper, zinc, cadmium, germanium, tin,antimony and bismuth; certain nitrides such as boron nitride; andsemi-conductors such as siliconcontaining substances. These materialsmay take any of the many forms conventional in the art such as rods,compacts, powders, pastes, and the like.

When the depolarizer or its reduction product is less soluble, depositsmay precipitate on the electrode surface and possibly block the cathodethereby preventing further reaction. Thus, under these conditions, highsurface area cathode design is preferable in order to provide maximumcapacity of the cathode. Moreover, where the oxidized state is lesssoluble, the depolarizer may be compounded together with the cathodematerial.

A high surface area cathode in combination with an alkali metalelectrolyte offers other advantages where one of the depolarizer statesis less soluble. For example, if the reduced form of the cathodedepolarizer is insoluble, the discharge product is held on the electrodesurface where it can be reoxidized on the charge cycle without the masstransfer limitations associated with soluble reduced products. Thisfacilitates the rapid and efiicient recharging necessary for operationof the cells as secondary systems.

It will be evident from the foregoing discussion that cathode materialsmay vary widely with choice being limited, in soluble cathode productsystems, primarily only by the ability to conduct electrons and totransmit them to the depolarizer without substantially reacting withdepolarizer during the useful life of the battery, and in insolublecathode product systems, additionally by the form of the cathodematerial, i.e., it should have high surface area.

To obtain these advantages, any of the aforementioned cathode materialsmay be employed provided they are in a form in which surface area ismaximized, e.g., at least about 0.1 square meter per gram. Hence,powders, pastes, sintered materials, and the like, will be preferredover plates, disks, screens or expanded metal structures. Particularlypreferred are carbon in its many high surface area forms, e.g.,graphite, acetylene black, carbon black, and amorphous carbon; powderedplatinum, aluminum, nickel, tantalum and powdered or porous forms ofcathode materials previously mentioned; and combinations of theforegoing, such as carbon paste over a screen of platinum, aluminum, orother conductor.

The preferred embodiment of the invention is, of course, a cellemploying an alkali metal anode and an alkali metal electrolyte,particularly lithium or sodium.

The electrolyte salts employed in the practice of the present inventionare salts which dissolve and dissociate in the sulfur dioxide solutionand which are substantially inert to interaction with the electrodematerials and with sulfur dioxide, such as chemical oxidation by sulfurdioxide or coagulation or precipitation by sulfur dioxide. Such saltsare employed singly or in mixtures of two or more and in amountssufficient for dissociation in the sulfur dioxide solution and toprovide a useful specific conductivity. Specific conductivity, since itis a function of temperature as well as relative proportions of salt andsulfur dioxide solution, may vary widely. Generally, however, thespecific, conductivity of the mixture of sulfur dioxide solution andelectrolyte salt should be at least about 5 X 0- cm? at 22 C.

Electrolyte salts which are particularly preferred because of theirexceptionally high conductivity, solubility in the sulfur dioxidesolution and relative inertness to the electrode materials are lithiumperchlorate and lithium halides, particularly lithium bromide. Theseelectrode materials have been found to be particularly useful forreversible cells.

Also satisfactory as electrolytes are lithium salts of organic acidssuch as trichloroacetic, trifiuoroacetic, boric, formic, paratoluenesulfonic acids, and lithium tetrafiuoroborates, hexafluoroarsenates,hexafiuorophosphates, hexafluorosilicates, monofluoroacetates,chloroaluminates and bromoaluminates.

Electrolyte salts having cations other than alkali metals an operable,but are less preferred. Such salts are for example tetraalkylammonium,particularly tetra(1ower alkyl)ammonium, salts of halogens such aschlorine, fluorine, and bromine; tetraalkylammonium salts of organicacids such as trichloroacetic, trifluoroacetic, benzoic, formic,paratoluene sulfonic acid, and the like; and the tetraalkylammoniumtetrafiuoroborates, hexafiuoroarsenates, hexafluorophosphates,hexafluorosilicates, monofluoroacetates, chloroaluminates,bromoaluminates, and perchloroates. Nonlimiting examples of such saltsare tetraethylammonium chloride, tetraethylammonium acetate,tetrapropylammonium, tetrafluoroborate, tetrapropylammoniumhexafluorosilicate and tetraethylammonium tetrachloroaluminate.

In addition, tetraalkylammonium and metal salts of organic acids such asoleic, oxalic, palmitic, propionic, stearic, succinic, valeric,cinnamic; other metal halides, metal cyanates and thiocyanates; metalsulfites and sulfamates; and metal nitrates, dicyanamides andtricyanomethides are suitable. The metal cation in the foregoing saltswill preferably be an alkali or alkaline earth metal, provided thecathode has a large surface area. Also included but less preferred aresulfonium, arsonium and phosphonium salts such as trimethyl, triethyland tripropyl sulfonium halides, acetates and the like.

As already mentioned, when an atmospheric pressure system is desired,cosolvent is used with gaseous sulfur dioxide to promote solubility andconductivity of the electrolyte salts. Generally, the cosolvent issubstantially saturated with the gaseous sulfur dioxide. Such cosolventsmust be stable to the sufur dioxide and the other components of thesystem such as the electrolyte salts and electrode materials.

Generally, solvents which satisfy these requirements are liquid organicand inorganic compounds which have electron rich centers, i.e., containone or more atoms having at least one unshared pair of electrons, andwhich lack acidic hydrogen atoms. Such electron rich compounds arematerials which contain atoms of elements of Groups III IV V and VI ofthe Periodic Table [Handbook of Chemistry and Physics, 44th Ed. (1963),pp. 448-449] as, for example, boron, silicon, nitrogen, phosphorus,oxygen and sulfur as well as combinations of these elements. Organicsolvent molecules which are difunctional in these elements, i.e.,contain two or more of the foregoing elements whether identical ordifferent, are particularly suitable. By acidic hydrogen atoms is meanthydrogen atoms directly bonded to atoms of elements, except carbon, ofthe foregoing Periodic Groups. Thus, examples of excluded radicals wouldbe OH, SH, PH and NH. Hence, piperidine would be excluded butN-methylpiperidine would be included as operable. Solvents which arestrongly basic are not desirable.

The following classes of compounds exemplify organic cosolvents. Theseexamples are, of course, nonlimiting since it will be immediatelyobvious that other solvents of these classes are substantiallyequivalent although some will be preferred over others due to a greaterdegree of solubility, etc. Mixtures of two or more of these solvents maylikewise be employed.

Trialkyl borates: trimethyl borate, triethyl borate z 5 )s etc.; Boronicacid esters: dimethyl boronate C H B z sh, etc.; Borinic acid esters:methyldiethyl borinate (C H )BOCH etc.; Tetraalkyl silicates:tetramethyl silicate (CH O) Si,

etc.;

Alkylalkoxy silanes: methyltrimethoxy silane Nitro alkanes:nitromethane, nitroethane, etc.;

Alkylnitriles: acetonitrile, propionitrile, isobutylronitrile,

pivalonitrile, etc.;

Dialkyl amides: dimethylformamide (CH NCHO, di-

ethylformamide, etc.;

Lactams: N-methylpyrrolidinone also described as N-methyl-w-butyrolactam, N-methyl-B-propiolactam, N-methyl-a-valerolactam, etc.;

Tetraalkyl ureas: tetramethylurea (CH NCON(CH etc.;

Acetals: dimethylacetal CH CH(OCH etc.;

Ketals: 2,2-dimethoxypropane (CH O) C(CH etc.;

Monocarboxylic acid ester: ethylacetate, ethylbutyrate,

etc.;

Orthoesters: trimethylorthoformate HC(OCH triethylorthoacetate CH C(OC Hetc.;

Lactones: 'y-butyrolacetone, 'y-valerolactone; etc.;

Dialkyl carbonates: dimethyl carbonate, diethyl carbonate, etc.;

Alkylene carbonates: ethylene carbonate, propylene earbonate, etc.;

Orthocarbonates: tetramethyl orthocarbonate, etc.;

Monoethers: dimethyl ether, diethyl ether, diisopropyl ether,n-butylether, the aliphatic monoethers disclosed as solvents in US.Pats. 2,019,832 and 2,171,867, etc.;

Polyethers: ethylene glycol diethyl ether, diethylene glycol diethylether, dimethoxytetraethyleneglycol, 1,2-dimethoxyethane (glyme), thealiphatic polyethers disclosed as solvents in US. Pats. 2,023,793 and2,171,- 867, etc.

Cyclic ethers: tetrahydrofuran, 1,4-dioxane, tetrahydropyran, etc.;

Monocarboxylic acid anhydrides: acetic anhydride, propionic anhydride,etc.;

Dialkyl sulfates: dimethylsulfate, etc.;

Dialkyl sulfites: dimethylsulfite, etc.;

Alkylene sulfites: ethylene sulfite, propylene sulfite, etc.;

Dialkyl sulfinites: dimethylsulfite, etc.;

Alkyl sulfonates: methylethyl sulfonate C H SO OCH etc.;

Nonlimiting examples of inorganic cosolvents are phosphorus oxychloride,thionyl chloride and sulfuryl chloride. Other such solvents aredescribed in Audrieth and Kleinberg, Nonaqueous Solvents (1953),particularly at page 234, said text being incorporated herein byreference.

The relative proportions of sulfur dioxide, electrolyte salt, cosolventand soluble depolarizer are a matter of choice depending on thesolubility of the components in each other at a given temperature andpressure. Preferably, sufiicient amounts of sulfur dioxide are employedto substantially saturate the cosolvent. The relative and total amountsof sulfur dioxide. cosolvent and electrolyte salt will be such as tosubstantially dissolve the electrolyte salt and to achieve substantialmutual solubility as well as to provide a useful specific conductivity.From about 0.01 to 5.0, preferably 0.1 to 2.0, molar solution of theelectrolyte relative to the cosolvent will generally contribute to therequisite solubility and conductivity in combination with the sulfurdioxide solution. But obviously the concentration may be variedsubstantially according to the conductivities desired since specificconductivity is a function of temperature as well as concentration ofmaterials in the solvent-electrolyte system.

When a cosolvent is employed, as in a room temperature-atmosphericpressure system, the cosolvent may be first saturated with the gaseoussulfur dioxide and the electrolyte salt added, or the salt may bedissolved in the cosolvent and sulfur dioxide bubbled through themixture. Complete saturation with sulfur dioxide is not critical sincefor given electrolyte and cosolvent, concentrations of sulfur dioxidesubstantially less than saturation values at various temperatures andpressures contribute to a useful specific conductivity and cathodecurrent density. Alternatively, systems containing amounts of sulfurdioxide greater than that required for saturation at atmosphericpressure may also be employed although such systems must be maintainedat superatmospheric pressure. In general, amounts of sulfur dioxide fromabout 0.2 molar, relative to the cosolvent, up to saturation at a giventemperature will be useful.

Alternatively, the use of a cosolvent may be avoided by employing liquidsulfur dioxide under the requisite superatmospheric pressure or at aliquefying temperature and atmospheric pressure. Such a system isadvantageous due to the greater proportion of sulfur dioxide utilizedper unit volume and weight of cell and more intimate contact of thesulfur dioxide with the cathode. Substantially the same relative andtotal amounts of liquid sulfur dioxide and electrolyte salt will beemployed as described above with reference to the atmosphericpressure-dissolved sulfur dioxide system. If desired, a cosolvent mayalso be employed in this system to aid conductivity and dissolution ofelectrolyte salt but such, of course, is not required.

The amount of soluble depolarizer may vary widely but will generallyprovide cathode capacity about equal to anode capacity. 1

In the construction of the cells or batteries of the invention, a largevariety of cell enclosure materials is available, including inertmaterials such as glass, high density polyethylenes, polypropylenes,polytetrafluoroethylenes or the like. The cell is generally constructedso as to permit maintaining an inert atmosphere within the cell closurewhile excluding atmospheric moisture, nitrogen and oxygen. Inert gasessuch as argon, xenon and helium may be used for this purpose.Conventional means are provided for the addition and exit of the desiredgases and for the insertion of the electrodes. The electrodes areconstructed of the conductive materials noted above. In a typicalembodiment, the anode is inserted as a coil, plate or sheet of metal orit may be a bed of a saturated metal amalgam. When a superatmosphericpressure system is desired, the enclosure, of course, will be maintainedpressure-tight at the required liquefying pressure for sulfur dioxide.

Other aspects of cell construction such as the geometry of arrangementof electrodes Within the cell closure and size of electrodes are routineconsiderations and form no part of the present invention.

The cells or batteries of the invention may also be constructed asso-called "reserve cells or batteries. These are power supplies whichare manufactured and then stored in a form that insures inertness untila specific action is taken by the user or that results automaticallyfrom the application. In a simple form, the electrolyte may be separatedfrom the battery plates and later added when activation is desired.Activation of such reserve cells or batteries may be effected in otherknown ways. For example, activation may be manual as by simple immersionof the electrodes in the sulfur dioxide-electrolyte mixture or byhypodermic filling of a cell or battery with sulfur dioxide and/ orelectrolyte. Activation may be provided automatically as well, as from acondition of use, e.g., from the linear acceleration resulting frommissile launching or gun firing of a projectile which provides theenergy to break an electrolyte ampule. The nature of reserve batterysystems as Well as descriptions of particular forms of such systems aredescribed, for example, in The Encyclopedia of Electrochemistry, C. A.Hampel, editor, Reinhold Publishing Corporation (1964), pages 76-81.This publication is incorporated herein by reference. Many othervariations of cell or battery design will at once become obvious tothose skilled in the art in view of the present disclosure and theinvention is not, of course, limited to any one design.

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The cell solution was IM LiClO, in propylene carbonate and S togetherwith sulfuryl chloride. A lithium anode and a 2 cm. nickel plaquecathode were employed. The cell, at a concentration of depolarizer of3.3 M, gave an open circuit voltage of 3.5 volts and delivered ma./cm.at 2.9 to 3.5 volts for 2200 seconds.

It is understood that although all of the cells and batteries of theinvention as described and as illustrated by the foregoing examples areefiective for various applications without electrode separatormaterials, the invention also contemplates and includes cells andbatteries in which it may be desirable to employ the conventionalelectrode separator materials such as are described hereiuabove toachieve mechanical separation.

Moreover, in addition to completely nonaqueous systems, the invention isintended to include cells and batteries wherein minor amounts of waterare present in the mixture of electrolyte salt and sulfur dioxidesolution (and cosolvent if desired) since, in practice, it is oftendiflicult to achieve a completely nonaqueous state. The cells andbatteries of the invention therefore may be described as beingsubstantially non-aqueous, i.e., as containing no more than the minoramount of water which can be tolerated without harming the anode orother elements of the system.

We claim:

1. A nonaqueous electrochemical current producing cell comprising, incombination an alkali metal anode,

a porous electroconductive inert solid cathode permeable by theelectrolyte liquid and a nonaqueous liquid electrolyte contacting saidanode and cathode, said liquid comprising (i) a solvent which comprisessulfur dioxide and an organic liquid co-solvenr, (ii) a dissolvedelectrolyte salt inert to sulfur dioxide, and (iii) a dissolved cathodedepolarizer having redox potential more oxidizing than sulfur dioxide.

[2. A nonaqueous electrochemical cell defined by claim 1 wherein saidliquid electrolyte further comprises an organic liquid co-solvent.]

3. A cell defined by claim 1 wherein said anode metal is lithium.

4. A cell defined by claim 1 wherein said dissolved depolarizer is anelectroactive tertiary aromatic amine.

5. A cell defined by claim 4 wherein said soluble depolarizer isN,N,N',N'-tetramethyl benzidene.

6. A cell defined by claim 4 wherein said dissolved depolarizer isN,N,N',N'-tetramethyl di-imoniumdiphenoquinone diperchlorate.

7. A cell defined by claim 1 wherein said electrolyte salt is a lithiumhalide.

8. A cell defined by claim 7 wherein said halide is lithium bromide.

9. A cell defined by claim 1 wherein said electrolyte salt is lithiumperchlorate.

References Cited The following references, cited by the Examiner, are ofrecord in the patented file of this patent or the original patent.

UNITED STATES PATENTS 3,393,093 7/1968 Shaw et al 136-6 2,897,249 7/1959Glicksman et al. 136-137 X 3,121,028 2/1964 Story 136-6 3,248,265 4/1966Herbert 136-6 3,279,952 10/1966 Minnick 136-100 3,423,242 1/ 1969 Meyerset a]. 136-6 3,542,602 11/1970 Gabano 136-155 3,567,515 3/1971 Maricleet al 136-6 2,554,447 5/1951 Sargent 136-100 2,874,204 2/1959 Morehouseet al 136-100 3,043,896 7/ 1962 Herbert et al 136-6 3,125,467 3/1964Lawson et a1 136-83 OTHER REFERENCES Journal of the ElectrochemicalSociety, vol. 94, pp. 299- 308, Schaschl, E., et al., A Low TemperatureLiquid Sulfur Dioxide Battery, 1948.

ANTHONY SKAPARS, Primary Examiner US. Cl. X.R.

